The present invention relates to the purification of materials utilizing hydrate formation.
Hydrates are a group of molecular complexes sometimes referred to as clathrates or clathrate compounds. A wide variety of organic compounds are known to form such complexes. They are characterized by a phenomenon in which "two or more components are associated without ordinary chemical union through complete enclosure of one set of molecules in a suitable structure formed by another", Powell, J. Chem. Soc. (London), vol. 61, 1948. Gas hydrates may thus be regarded as solid solutions in which the hydrate former solute is held in the lattice of the solvent water.
Hydrates have been studied extensively in petroleum gas processing and refining because precipitated hydrates in pipelines pose a problem. Hydrates have also been studied for potential industrial application to processes such as sea water desalination and solution concentration.
U.S. Pat. No. 2,904,511 to Donath describes a process for producing desalinated water by forming a hydrate with salt water, separating the hydrate from the residual concentrated solution and decomposing the hydrate to recover purified water.
U S. Pat. No. 3,415,747 to Glew describes the formation of hydrates at low pressure, separation of the hydrate from the residual concentrated solution, and decomposition of the hydrate as a method either of producing purified water or of recovering solutes from dilute aqueous solutions.
U.S. Pat. No. 4,253,948 to Hardman and Schwerko describes the use of liquid carbon dioxide for extraction of nonpolar solutes from aqueous solutions followed by separation of the carbon dioxide solvent from the raffinate and formation of carbon dioxide hydrate from the extracted water by cooling the extract. By this method the water content of the extract is reduced, although the loading of the carbon dioxide solvent with the product solute is not significantly altered.
U.S. Pat. No 4,147,456 to Klass relates to a process for storing fuel gas by pumping the gas into the lower portion of a storage vessel where a solid fuel gas hydrate can form due to the vessel being positioned beneath the surface of a body of water. The lower zone has a higher pressure relative to the atmosphere and this pressure can be sufficient to cause hydrate formation of the fuel gas and water. The lower pressure at an upper zone causes decomposition of the solid hydrate to fuel gas and water. Fuel gas for use is removed from the upper zone.
U.S. Pat. No. 4,007,787 to Cottle describes a process for recovering natural gas from gas hydrate reservoirs by passing light hydrocarbons which do not form hydrates through the formation to dissolve and recover natural gas.
While the use of hydrates has been studied with regard to the formation of hydrate crystals and the physical separation of crystals from the concentrated solution which results from their formation, the prior art does not disclose the use of an additional solvent or adsorbant phase to extract desired products from the concentrated aqueous phase, this extraction occurring while the residual aqueous solution is still in contact with the hydrate, and being enhanced by the increase in solute concentration caused by hydrate formation. In addition, the prior art does not disclose the use of a single material which serves simultaneously both as a hydrate former and as an extractant to extract solutes from the residual aqueous phase.